Masked Booby

The First and Second Records of Masked Booby (Sula dactylatra) in British Columbia. By Rick Toochin: Published: October 14, 2024.

The Masked Booby (Sula dactylatra) is a tropical seabird species that is strictly oceanic with a breeding range in the United States that is apparently limited to 3 Hawaiian Islands; Kaula (200–400 pairs), Lehua (5–10 pairs) (Harrison 1990a), and Moku Manu, off Oahu (40 pairs) (Nelson 1978c). The Northwestern Hawaiian Islands populations total at least 6,770 birds (Harrison et al. 1983). This species has successfully nested on the Dry Tortugas (Clapp and Robertson 1986, Ogden 1991b).

 

Outside of the United States the Masked Booby breeds on islands off the Yucatan Peninsula, throughout the West Indies from the southern Bahamas to the Venezuelan coast, islands off the Brazilian coast, in the eastern Pacific on the Revillagigedo Islands (18°N 112°W), Clipperton Island (10°N 108°W), and San Ambrosio Island and San Felix Island west of Chile (26°S 80°W) (Nelson 1978c), and Malpelo Island (3° 59' N, 81° 36' W), where approximately 10 birds roost with some breeding (Grace and Anderson 2009).

The Masked Booby forages throughout the tropical oceans and nests on hundreds of islands between 30°N and 30°S (Nelson 1978c). One of the largest breeding populations (apart from Clipperton) is Boatswain Bird Island in the central Atlantic (8°S 14°W) (Grace and Anderson 2009). There are numerous small colonies in the archipelagos of the central and western Pacific, around the mouth of the Red Sea, the Chagos archipelago (7°S 72°E), and islands off northern Australia into Indonesia (Grace and Anderson 2009).  An apparently isolated colony reported northwest of Taiwan (Nelson 1978c).

 

The identification of the Masked Booby is covered in all standard North American field guides. This is the largest of the booby species with the total length of the males measuring 74–82 cm, females 75–86 cm; with males weighing 1,220–2,211 grams, females 1,470–2,353 grams; and birds having a wingspan of 152–155 cm (Sibley 2000, Grace and Anderson 2009, Dunn and Alderfer 2017).

 

Adult plumage is bright white except black to blackish-brown primaries, secondaries, humerals, and tail; white on wings restricted to marginal, lesser and median coverts, and some outer primary-coverts, the rest blackish brown to black; underwing has white coverts, remiges blackish distally and broadly tinged pale silver-grey on bases (Sibley 2000, Grace and Anderson 2009). The bill ranges from greenish yellow to bright yellow and is thick based, tapering down without much curvature (Roberson 1998); dark slate to black skin around eye extends narrowly to upper bill base and on the lores to the upper throat, less dark on chin and lores (Grace and Anderson 2009, Dunn and Alderfer 2017). Sexes not reliably distinguished by appearance, only by voice (Grace and Anderson 2009).

 

Juvenile plumage is dark chocolate to blackish except for white on the upper back which forms a broad conspicuous collar , and white breast (Pitman and Jehl 1998); the tips of the scapulars are frosted whitish grey-brown with less distinct pale tips to lesser coverts and on the back to the upper tail-coverts; these are more or less blotched dark brown on rear flanks and rear thighs, otherwise has all-white underparts, underwing-coverts white except for a dark carpal patch and narrow dark line the extends towards the base of the wing (Grace and Anderson 2009, Dunn and Alderfer 2017). As birds age, the upperparts (including marginal and lesser wing-coverts) acquire dark brown and white feathers in a chequerboard pattern (Grace and Anderson 2009).

The Masked Booby is most similar in appearance to the occasionally sympatric Nazca Booby (Sula granti), formerly considered a subspecies of the Masked Booby (Grace and Anderson 2009, Dunn and Alderfer 2017). The Masked is distinguished by its yellow (not orange/pink as in Nazca Booby), deeper, thicker bill, and generally larger size (Grace and Anderson 2009, Dunn and Alderfer 2017). The juvenile may be easily differentiated by the conspicuous white collar on the upper back of the Masked, which is generally incomplete or lacking in the Nazca Booby (Pitman and Jehl 1998). The two species may also be distinguished, to some extent, by geographic location. The Nazca Booby is primarily restricted to the eastern Pacific with its largest colonies in the Galápagos and Malpelo (Colombia). However, Nazca Boobies have bred in the Hawaiian Islands (Grace and Anderson 2009) and off the coast of California (Roberson 1998).

 

The Masked Booby is also similar to sympatric white morph of the Red-footed Booby (Sula sula), but differs with this species in its larger size, yellow bill (not blue as in Red-foot Booby), dark tertials, lack of black carpal on underwing, and olive/khaki/purple/lead/orange feet (not red) (Sibley 2000, Grace and Anderson 2009, Dunn and Alderfer 2017). The thick bill and overall coloration are similar to that of gannet species (Morus sps) which are not found in British Columbia waters or close to the west coast but do occur on the east coast of North America and in the southern oceans (Grace and Anderson 2009, Dunn and Alderfer 2017). Juvenile Masked Booby may be confused with immature Northern Gannet (M. bassanus) off the East Coast of North America (Sibley 2000). The Masked Booby juvenile has a bright white breast with the Northern Gannet having a breast that is speckled to black, and a uniformly dark rump and tail (Dunn and Alderfer 2017). The Northern Gannet has a white “V” pointing toward the tail (Sibley 2000). The juvenile Masked Booby is best separated from that of the Brown Booby (Sula leucogaster) by a clean white breast and belly, from an adult Brown Booby by a smaller hood and whiter on the underwing including many primary-coverts (Grace and Anderson 2009, Dunn and Alderfer 2017). The Masked Booby can be separated from the similar looking juvenile Blue-footed Booby (Sula nebouxii) by much whiter coloration on the underwing and a smaller hood not reaching to the chest (Sibley 2000). In a ventral view some subadults might be confused with an adult Blue-footed Booby, differing slightly in underwing pattern, and color of feet and bill useful in very good views (Grace and Anderson 2009).

Subspecies are designated based on soft body part color, which varies regionally, and molecular evidence of mitochondrial variation at the cytochrome-b gene (Friesen et al. 2002). Recognized subspecies vary, but most recent treatments have designated four subspecies (Clements et al. 2023). The first subspecies of Masked Booby is (Sula dactylatra dactylatra) whichbreeds on islands in the Caribbean and off the north coast of South America south to Eastern Brazil, on Ascension Island in the South Atlantic Ocean, and possibly also still in Bahamas has a straw-colored bill with orange to olive legs and feet); the second subspecies is (Sula dactylatra melanops)which found on islands from the southern Red Sea region and western Indian Ocean has a bill that is orange-yellow to yellow-green, legs and feet lead gray to khaki-olive, the tarsi is often grayer, and the central tail feathers have little or no silvery gray colour with birds of the eastern Indian Ocean having blue legs and feet are sometime classified as its own subspecies (S.d. bedouti); the third subspecies is (Sula dactylatra personata) is found in Australasia to the central Pacific Ocean and has yellow bill, iris tends to be orange-yellow or amber, olive drab to bluish-gray legs and feet; the fourth subspecies is (Sula dactylatra tasmani)which has also been in the past referred to as (S. d. fullagari) is found in the Tasman Sea has a brown iris, all other subspecies have a yellow iris, bill  straw-yellow to olivaceous greenish yellow, legs dark khaki-gray, grayer on tarsi (Grace and Anderson 2009). The name fullagari was previously applied to a form mistakenly believed extinct (Tasman Booby, S. tasmani), which has now been reclassified on basis of morphological and genetic data as a race of present species (Steeves et al. 2010, Ismar et al. 2010). Subspecific designation of (S.d. bedouti) is debated, with some authors placing it within (S.d. personata) (O'Brien and Davies 1990). Birds of the northeastern Pacific are sometimes separated as race (S. d. californica), but extensive individual variation means no consistent significant differences detected, so best treated as a synonym of (S. d. personata) (Pitman and Jehl 1998).

 

Any Booby species encountered in British Columbia should be documented as thoroughly as possible with photographs and accompanying field notes. If the documentation is good enough, then subspecies distinction could be possible but can not always be expected.

Along the west coast of North America, the Masked Booby is a casual to accidental vagrant species. In California, there are 43 accepted records by the California Bird Records Committee with records occurring throughout the year (Hamilton et al. 2007, Tietz and McCaskie 2020). The only record accepted record for Oregon by Oregon Bird Records Committee is of an immature bird found emaciated and later died in captivity in North Portland in Multnomah County on 15 August 2006 (OBRC 2020). In Washington, there are no definitive records of Masked Booby but there is 1 accepted record by the Washington Bird Records Committee of a Nazca/Masked Booby photographed off Discovery Park in Seattle in King County on July 20, 2022 (Wahl et al. 2005, WRBC 2022). There are no records for Alaska (Gibson et al. 2023)

 

In British Columbia, the Masked Booby is an accidental vagrant and was only recently added to the avifauna of the province. The only confirmed record was of an adult found and photographed by William Woodbury 5-10 nautical miles offshore between Frederick and Langara Islands off Haida Gwaii on September 21, 2021 (BCBAB 2023). A clear photograph of the bird was posted to the BC Bird Alert Blog and can be seen here: https://bcbirdalert.blogspot.com/2023/10/rba-brown-booby-in-haida-gwaii-and-bcs.html. A second record for the province was found and photographed Sebastián Pardo from the deck of the CCGS Sir John Franklin in Queen Charlotte Sound North of Cape Scott at coordinates [50.937, -128.305] on October 8, 2024 (e-bird 2024). A photograph of the bird can be found at https://ebird.org/checklist/S198078262 (ebird 2024).

 

There is also a report of an adult observed by Roger Taylor and Neil Robins flying over the Top Bridge Trail, in Parksville on May 23, 2007 (Cecile 2007b, Toochin and Cecile 2023). Though there are no photographs of this bird a detailed description of the bird was provided to the author and is included here as a good sight record (Cecile 2007b). 

This species is likely to turn up again along the British Columbia coast and should be watched for in the future. 

I want to thank Don Cecile for editing the original manuscript.

 

BCBAB. 2023. BC Bird Alert Blog: RBA: BROWN BOOBY in Haida Gwaii - Oct 26th and BC’s 1st record of MASKED BOOBY! Retrieved from https://bcbirdalert.blogspot.com/2023/10/rba-brown-booby-in-haida-gwaii-and- bcs.html [Accessed: December 16, 2023].

Cecile, D. 2007b. Winter season- British Columbia. North American Birds 61: 314-315.

Clapp, R. B. and Jr. Robertson, W. B. 1986. Nesting of the Masked Booby (Sula dactylatra, new record) on the Dry Tortugas, Florida: The first record for the contigous USA. Colon. Waterbirds 9: 113-116.

Clements, J. F., P. C. Rasmussen, T. S. Schulenberg, M. J. Iliff, T. A. Fredericks, J. A. Gerbracht, D. Lepage, A. Spencer, S. M. Billerman, B. L. Sullivan, and C. L. Wood. 2023. The eBird/Clements checklist of Birds of the World: v2023. [Online Resource] Retrieved from https://www.birds.cornell.edu/clementschecklist/download/ [Accessed: December 17, 2023]

 

Dunn, J. L. and J. Alderfer. 2017. National Geographic Field Guide to the Birds of North America. National Geographic Society, Washington D.C. 574pp.

 

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